1. Field of the Invention
The present invention relates generally to an etching process for fabricating semiconductor components and in particular, to a method of detecting an etching end-point during a process of etching objects to yield a desired pattern using a mask. More specifically, the present invention relates generally to a method of detecting an etching end-point at which the size of a remaining object covered by a mask reaches a target size.
2. Description of the Related Art
A laser diode has an active layer with a narrow width in which a laser oscillates which is formed by growing a multi-quantum well (MQW) on a wafer using a metal-organic chemical vapor deposition (MOCVD) technique or a molecular beam epitaxy (MBE) technique.
In order to fabricate an active layer of a laser diode, first, an active layer is grown on an n+ type semiconductor substrate using the MOCVD technique or the MBE technique, and a p+ type semiconductor clad for current supply is layered on the active layer. Second, a mask layer of a dielectric substance such as SiO2 or SiNx is layered on the clad to form a mask. Third, the mask (the patterned mask layer) is formed by etching the mask layer to represent a predetermined rectangular pattern using a photolithography process. Fourth, the active layer and clad are dry-etched or wet-etched to represent the predetermined rectangular pattern using the mask. The width of a remaining active layer covered by the mask is generally 1 to 1.6 μm to maintain a single mode, while the width of a spot size converting region is generally 0.4 to 0.6 μmin in a case where the spot size converting region is formed on an edge of the remaining active layer to easily arrange with an optical fiber.
In addition, a mask may be formed on an active layer, and a clad may be layered after the process of etching the active layer is finished.
In the active layer etching process, since an etching speed is not fixed and an interface state between the clad (or active layer) and the mask is not uniform, the width of the remaining active layer obtained through the etching process is not uniform even if the same mask is used. As such, it is common that an etching time is shorten and necessary to determine whether a desired target size is achieved by observing the width of the remaining active layer and the width of the mask using a microscope. Further, an additional etching process is required in a case where the width of the remaining active layer is formed more widely than the norm.
When a computer simulation of the remaining active layer is performed to estimate a laser oscillation characteristic and a far field pattern (PPF), a tolerance width of the remaining active layer to obtain the desired characteristics is ±0.1 μm. However, when the width of the remaining active layer is observed through an optical microscope using a visible ray, it is difficult to exactly know the width of the remaining active layer as it is difficult to distinguish a difference of below 0.2 μm. Accordingly, when laser diode components are fabricated, the laser oscillation characteristic and the PPF are frequently off from the desired outcome.
As described above, the conventional method of detecting an etching end-point using an optical microscope is not accurate. Accordingly, there is a need for an improved method of detecting an etching end-point with more accuracy.